1. Field of the Invention
This invention relates to a mixture gas heating device for the mixture gas to be introduced into an internal combustion engine, and more particularly to a device for heating a suction manifold by means of exhaust gases from an internal combustion engine.
2. Description of the Prior Art
In general, heating of mixture gas to be introduced into an internal combustion engine plays an important role in improvements of the fuel consumption rate as well as purification of exhaust gases. Particularly, the maintenance of the suction manifold at a suitable temperature is of consequence. More specifically, when the temperature is too low, then there may not be obtained satisfactory fuel evaporation, while too high a temperature will result in the lowered output or impaired durability of the suction manifold. In other words, control of the mixture gas heating level is of supreme importance.
In the mixture gas heating device for use in the prior art internal combustion engine, the change-over valve for use in heating mixture gas due to exhaust gases is provided within an exhaust manifold. Thus, the change-over valve is exposed to a high temperature all the times, resulting in poor durability. In other words, the change-over valve provided within the exhaust manifold is so designed as to switch the direction of exhaust gas flow from one to another depending on the warm-up condition of an engine or on the temperature condition in the suction manifold. However, since the valve stem of a change-over valve is positioned within the exhaust manifold, the valve is apt to undergo thermal strain or oxidation or corrosion, thus being plagued with difficulties in obtaining a change-over valve which gives smooth operation and sufficient durability and reliability.